This invention is directed to the use of phosphotyrosine phosphatase inhibitors for controlling cellular proliferation, particularly proliferation of B lymphocytes.
Tyrosine phosphorylation is known to play an essential role in the control of lymphocyte function. This control is exerted by a network of tyrosine kinases and phosphotyrosine phosphatases.
Two different processes known to induce B cell apoptosis have been shown to act through tyrosine phosphorylation.
Apoptosis is a pattern of programmed cell death that involves the breakup of the cellular DNA and can be recognized by electrophoresis of the DNA of the cells. When apoptosis occurs, the DNA is broken into fragments, which can be detected as a ladder on electrophoresis.
In immature B cells, stimulation of sIgM (surface immunoglobulin M) by either antigen or anti-immunoglobulin antibodies activates the cells (G. J. V. Nossal, Annu. Rev. Immunol. 1:33-62 (1983)). Stimulation of sIg (surface immunoglobulin) on B cells induces tyrosine phosphorylation (M. R. Gold et al., Nature 345:810-813 (1990); M. A. Campbell & B. M. Sefton, EMBO J. 9:2125-2131 (1990)), which is essential for productive sIg signaling (P. J. L. Lane et al., J. Immunol. 146:715-722 (1991)). As a result of sIg stimulation, Src family kinases are activated (A. L. Burkhardt et al., Proc. Natl. Acad. Sci. USA 88:7410-7414 (1991)). Furthermore, expression of the Src family tyrosine kinase Blk was found to be essential in B cell lymphomas where sIgM stimulation leads to growth arrest and apoptosis (X. R. Yao and D. W. Scott, Immunol. Rev. 132:163-186 (1993)). Thus, on sIgM stimulation, tyrosine kinases such as Blk phosphorylate one or more proteins on tyrosine residues, and once phosphorylated, these proteins are then able to induce apoptosis. However, it has also been shown that the abundant phosphotyrosine phosphatase CD45 is required for sIg signal transduction (L. B. Justement et al., Science 252:1839-1842 (1991)).
Ionizing radiation is standard therapy for B cell malignancies such as leukemias and lymphomas. It has been demonstrated that ionizing radiation stimulates B cell tyrosine kinases, triggering apoptosis and clonogenic cell death (F. M. Uckun et al., Proc. Natl. Acad. Sci. USA 89:9005-9009 (1992)). In this study, the phosphotyrosine phosphatase inhibitor vanadate, administered alone, was not effective. The activation of tyrosine kinases by ionizing radiation was essential for the induction of apoptosis because the tyrosine kinase inhibitors genistein and herbimycin A blocked the effects of the radiation.
In addition to blocking proliferation of malignant B cells in diseases such as leukemias and lymphomas, in a number of situations it may be desirable to slow the growth and/or differentiation of normal B cells. Such occasions include organ transplantation, in which the immune response, at least in the short term, must be suppressed. Limited control of the proliferation of B cells may also be desirable in the treatment of autoimmune diseases such as rheumatoid arthritis and lupus erythematosus.
Accordingly, there exists a need for improved methods of controlling proliferation of B cells in malignant and non-malignant conditions without requiring the use of radiation. Such an approach preferably involves the induction of programmed cell death (apoptosis) in susceptible cells.